Table I - National standards maintained at the ENEA-INMRI (Italy) in the field of neutron metrology. Am-Be and 252 Cf neutrons.

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1 CCRI(III)/15-20 Report to the CCRI Section III on the activity carried out at the ENEA-INMRI on neutron measurements in Lina Quintieri and Pierino De Felice Istituto Nazionale di Metrologia delle Radiazioni Ionizzanti ENEA, C. R. Casaccia P.O. Box 2400, I Rome (Italy) 1. INTRODUCTION The ENEA-INMRI The National Institute of Ionising Radiation Metrology (INMRI) belongs to the Italian National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA). Based on the role given by the Italian Law No. 273/1991, the ENEA-INMRI is responsible for developing and providing the Italian national standards related to the ionising radiation quantities. The metrological activities at ENEA-INMRI are carried out along the following lines: Therapy level and industrial radiation processing dosimetry standards; Protection level dosimetry standards; Radionuclide standards; Neutron standards. The ENEA-INMRI scientific programmes are focused on developing and maintaining the national standards for ionising radiation measurements and on the more general activities in the field of standardisation and quality-assurance for ionising radiation measurements. A calibration service for instruments used in this field is also performed at ENEA-INMRI, according to the MRA, for medical, research, industrial and radiation protection purposes. The ENEA-INMRI national standards include about 20 experimental lines for absolute measurements of ionising radiations. These are complemented by irradiation facilities (for alpha, beta and gamma radiation), x-ray generators, neutron and many radionuclide sources and a 20 MeV electron accelerator. ENEA-INMRI Neutron metrology The ENEA-INMRI activities in the field of neutron metrology started already in A number of standards were developed in the following 10 years and compared at international level [1, 2]. The main characteristics of these standards are reported in Table I. Table I - National standards maintained at the ENEA-INMRI (Italy) in the field of neutron metrology. Quantity Standard Radiation Quality Uncertainty ( ) Measurement range Neutron emission -Manganese Sulphate Bath Am-Be and 252 Cf neutrons 1.5 ( ) s -1 -Long Counter * " 1.7 ( ) s -1 Neutron Flux -Thermal Neutron Flux Density Thermal Density Standard ** neutrons cm -2 s -1 * High precision secondary standard (De Pangher long counter, acquired in the 70 s). ** Six Am-Be neutron sources with graphite and polyethylene moderator and gold foil activation measuring method. ( ) The uncertainty values are relative (%) combined standard uncertainties (k=1). The new neutron laboratory is located in an ex greenhouse refurbished using low neutron scattering material and provided with a false floor, 3 m above the ground, on which the neutron monitor calibration system has been arranged. In this way low neutron scattering conditions are established. A neutron source storage is located below the light floor, as well as the primary standards room (manganese bath and thermal flux density). Several radionuclide neutron sources (Table III), with Pag. 1/8

2 maximum individual emission rate of about /s, are available that are usable for instrument calibration. In addition, the ENEA-INMRI can rely on a number of neutron sources and/or irradiation facilities managed by other ENEA Technical Units such as: a TRIGA Reactor (1 MW, cm -2 s -1 ), a TAPIRO Reactor (5 kw, cm -2 s -1 ) and the Frascati Neutron Generator (14 MeV, s -1 ). A commercial Thermo generator of 14 MeV neutron beam is considered as a possible additional reference field: this source is made available by the UTFIS department of ENEA, in the frame of a collaboration agreement, and is going to be characterized for metrological purposes. This activity will foresee to use the De Pangher long counter, that is going to be putted again into operation before the end of this year. Table III Radionuclide neutron sources available at the ENEA-INMRI for neutron metrology. Purchase year: Source type Neutron emission rate (s -1 ) Am-Li 1.0 E+05 Am-F 4.5 E+05 Am-B 4.0 E+05 Am-Be 2.4 E+06 Am-Li 4.0 E+04 Am-Be 2.4 E+06 Am-Be 2.4 E+06 Am-Be 7.2 E+04 Cf-252 (*) 6.9 E+04 Cf-252 (*) 2.9 E+03 Cf-252 (*) 1.2 E+02 Cf-252 (*) 4.6 E+01 Po-Li 1.3 E+01 (*) The Cf-252 neutron sources have decayed down to too low emission rates values and are no longer usable. Purchase of a new source is planned for The present report summarizes the activities carried out at the ENEA-INMRI in the field of interest of CCRI(III): Neutron measurements. Furthermore the ongoing activities and the future plan will be briefly described. 2. DEVELOPMENT OF PRIMARY STANDARDS AND COMPARISONS MnSO 4 bath The ENEA-INMRI 1973 neutron emission rate primary standard (MnSO 4 bath) [3] was redrawn. It consists of a stainless steel spherical tank (1 m external diameter, 5 mm thickness), filled with MnSO 4 solution (about 550 L, 1.2 M in MnSO 4 ). A motorized source lifting system and an external circuit, equipped with a circulation pump, 1 L Marinelli beaker and NaI(Tl) detector, were added, recently, as shown in Figure 1. During 2012, as part of the work done for a Nuclear Engineering master thesis, the first measurement activities have been carried out with the new assessed standard and two main complementary tasks have been achieved: (a) MCNP 5 Monte Carlo simulations for different system configurations aiming at the determination of the main corrections for data evaluation; (b) NaI(Tl) detector calibration carried out by the introduction in the bath of a well known 56 Mn activity (obtained by 55 Mn irradiation in the neutron thermal beam of the ENEA TRIGA reactor and measured by the ENEA-INMRI radionuclide activity standards). Pag. 2/8

3 The first neutron emission rate measurements were carried out in 2012 for two AmBe sources [4]. One of these sources had been already calibrated at NPL in Figure 1 - Scheme of the ENEA-INMRI modified MnSO 4 bath. M=stepper motor, S=sample holder, P=pump (2000 L/h), V=Valves, B=Marinelli Beacker and NaI(Tl) detector. The new calibration result is in good agreement with the old one. The absolute emission rates of the two newly standardized neutron sources were also compared each other by the Long Counter system finding a good agreement. Figure 2 Scheme of the ENEA-INMRI thermal neutron flux density standard. 1: graphite cylinder; 2: polyethylene reflector; 3: neutron sources; 4: air cavity; 5: polyethylene-graphite plug. All dimensions are expressed in mm. Pag. 3/8

4 Thermal neutron flux density standard The thermal neutron flux standard (Figure 10) was assembled in 1973 [5]. It consists of a reactor grade graphite cylinder (25 cm diameter, 20 cm high), surrounded by a 13.5 cm thick polyethylene reflector, which acts as moderator and shield. Six 241 Am-Be neutron sources (with an average individual emission rate of about 10 6 s 1 ) are located in the polyethylene reflector at angular distances of 60 o, one from the other. The source centers are placed in a plane crossing perpendicularly, in its center, the vertical axis of an irradiation cylindrical air cavity (5 cm diameter, 10 cm height). A movable polyethylene-graphite plug closes the access to the irradiation cavity. The standard was calibrated the first time in 1974 [6] by the foil activation technique, giving a flux value (or, equivalently, fluence rate) of cm 2 s 1 with 0.9% (1σ) uncertainty. The foil activity measurements are traceable to the national standard of radionuclide activity (Bq). The accurate characterization of the spectrum inside the cavity by means of the foil activation method is an important activity started in 2014 and it is still in in progress. The thermal and epithermal components are determined following the ASTM E262 standard ( Standard Test Method for Determining Thermal Neutron Reaction Rates and Thermal Neutron Fluence Rates by Radioactivation Techniques ), while the foil activation is measured by the secondary standard HPGe or, otherwise, using the absolute 4 πβγ method (relying on the Radionuclide service inside the ENEA-INMRI institute). Table IV Thermal and epithermal components of the neutron spectrum in the ENEA-INMRI thermal standard. In the last column the Cd ratio has been reported. (This activity is still in progress, to refine more accurately the energy spectrum) Foil mat Diameter [mm] mass [g] Cd clad. (1mm) t_irr (min) A0 (Bq) Φ 0 [cm -2 s -1 ] Φ e [cm -2 s -1 ] R= (A s /A Cd ) Au Au 20 mm g 20 mm g N ±0.7% Y ±2.3% ±1% Au Au 10 mm g 10 mm g N ±3% Y ±2% ± 2% A detailed analysis of the preliminary results and an exhaustive description of the method applied has been reported as internal report [7] of ENEA, whereas a scientific publication on review will be submitted as soon as the concerned Monte Carlo predictions will be ready for comparison (FLUKA,MCNPX), in order to fix some issues in the obtained experimental results. In the frame of the future activities, a feasibility study of a new thermal pile is in progress. This study concerns the design of a thermal neutron irradiation system for calibration of personal dosimeters in terms of H p (10). The main goal is to realize a 35 cm diameter cylindrical air cavity (to allow the uniform irradiation of 30cm x30cm x15 cm water slab phantom, according to what stated on Hp(10) by International Standard ISO ). The thermal cavity should have at least a neutron fluence rate around cm -2 s -1 and a thermal fluence homogeneity within few percent. At present, parametric Monte Carlo estimations are in progress to optimize the shape, material thickness, source (AmBe) distribution and numbers in order to maximize the thermal flux density Pag. 4/8

5 inside the column. The spatial uniformity is also an important constraint in defining the final optimized solution. 3. CALIBRATION ACTIVITY Neutron calibration facility Since 2008, the neutron laboratory is equipped with a completely new automated system for neutron monitor calibration (see Figure 9). Neutron detectors are presently calibrated using an 241 Am-Be source with emission rate of (2.24 ± 0.03) 10 6 s 1, as recently assessed in [4]. The ISO procedure based on the Reduced Fitting method is applied for calibration. Neutron monitors are placed on a finely tunable irradiation bench and aligned with the neutron source using an optical laser beam. When all it is ready for the measurement, a software written in VC++ controls the source ejection and rotation (to compensate the source emission anisotropy), inhibits the laboratory access and acquires the instrumentation lectures at several test points along the irradiation bench. After an optimized time interval to get a stable device lectures (depending also on the detector time response characteristics), the instrument position is changed and a new acquisition starts. The system can also be remotely controlled by web connection. A dedicated analysis software provides the data fitting and computes the room-scattering corrections, the virtual detector center and finally provides the calibration factor as defined in ISO A suitable 137 Cs source is going to be used to check the survey meter sensibility to gamma response. In order to determine with the best accuracy the reference neutron field obtained with the AmBe source, the INFN-LNF Bonner sphere spectrometer will be used, in an ongoing experimental measurement campaign (scheduled by the end of June 2015). In addition, the room scattering radiation contribution measurement, by using ISO compliant shadow cones (always in collaboration with INFN-LNF), has been planned. This requires equipping the laboratory of a new automating system for suitably centering and moving the cones in between the source and the survey meters. A new format for the released calibration certificates has been assessed and is currently in use. Since 2013 up to nowadays 10 survey meters have been calibrated by the neutron metrology service, mainly for national research institutes and also for several hospitals. The covered dose equivalent range goes fro 8 μsv/h up to 350 μsv/h. Quality system The ENEA-INMRI quality system (in agreement with ISO standard) was completed with the new neutron calibration services. A quality system peer review was successfully performed in 2012 in the frame of EURAMET project n.1123 On site peer review among Portugal, Spain and Italy. 4. PARTICIPATION IN METROLOGICAL AND STANDARDISATION ORGANISATIONS Part of the time was devoted to activity in metrological and standardisation organisations: ICRM, IEC/TC45, ISO/TC85/SC2, UNI (National Standardisation Organisation). The ENEA-INMRI attended the BIPM/CCRI-III meeting for the first time in April 2013, as observer. This participation will complement those in CCRI Sections I and II in which ENEA-INMRI delegates and experts are members since long time. The ENEA-INMRI attended the 2015 BIPM/CCRI-III meeting as member for the first time since long time. Pag. 5/8

6 5. TEACHING IN ACADEMIC SCHOOLs AND UNIVERSITIES CCRI(III)/15-XX Teaching activities have been conducted for the Rome University La Sapienza, especially for nuclear engineers and Health Physic courses for University of Tor Vergata (Lecutrers on the following topics: (a) neutron sources, (b) neutron interaction with matters, (c) neutron detectors and (d) neutron dosimetry). 6. RESEARCH PROJECTS IN THE FIELD OF IONISING RADIATION The ENEA-INMRI is involved in several European projects in the EMRP frame (Table IV) as well as in the FP7 Programme. Table IV EMRP Projects in which the ENEA-INMRI participates. Programme Project title EMIR -PRT Metrology for accuracy of dose to patients in hadron therapy (Task on the unwanted dose neutron estimation in accelerator driven sources) H2020 MONSTRE project, Call SPACE 2015 INFN-LNF Collaborations on several experimental and MC simulations activities 7. NEUTRON METROLOGY STAFF Istituto Nazionale di Metrologia delle Radiazioni Ionizzanti ENEA, C. R. Casaccia, P.O. Box 2400, I Rome (Italy) STAFF (1) username (2) Phone Fax extension Director Dr. P. De Felice pierino.defelice Scientists Dr. L. Quintieri lina.quintieri (1) Administrative service and technical assistance for maintaining and repair are supplied by the CR Casaccia central service. Some activities at the ENEA-INMRI in the period have been carried out with the collaboration with an engineer from TRIGA reactor service. (2) enea.it Due to some restructuration and reorganization still in progress in the ENEA Agency, the staff at present working in the neutron metrology laboratory is limited to one person, but a technician and a physicist should join the laboratory by the end of Anyway the support of other internal metrological services (mainly, radionuclide and high dose level dosimetry), in addition to the synergic and fruitful collaboration with some scientists from the TRIGA reactor and INFN-LNF allow progressing regularly and continuously in the planned work of the Neutron Laboratory. 8. SCIENTIFIC PUBBLICATION since ) A.Pietropaolo, F.Murtas, G.Claps, L.Quitnieri, D.Raspino, G.Celentano, A.Vannozzi, O.Frascsiello, A new 3He-free thermal neutrons detector concept based on the GEM technology, Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment (Impact Factor: 1.32). 07/2013; 729:117. DOI: /j.nima Pag. 6/8

7 2) M.Ferrario,.L.Quintieri et al., IRIDE: Interdisciplinary research infrastructure based on dual electron linacs and lasers, Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment (Impact Factor: 1.32). 03/2014; 740: DOI: /j.nima ) G.Claps, F.Murtas, A.Pietropaolo, G.Celentano, A.Vannozzi, A.Santoni, L.Quintieri, L.A.Riedele, 3He-free triple GEM thermal neutron detector, EPL (Europhysics Letters) (Impact Factor: 2.27). 12/2013; 105(2). DOI: / /105/ ) R. Bedogni, J.M.Gómez Ros, A.Pola, M.V.Introini, D.Bortot, A.Gentile A.Esposito, G. Mazzitelli, B.Buonomo, L.Quintieri, L.Foggetta, Testing a newly developed single-sphere neutron spectrometer in reference monochromatic fields from 147 kev to 14.8 MeV, Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment (Impact Factor: 1.32). 01/2013; 714(110):114. 5) M. Prata, D. Alloni, P. De Felice, M. Palomba, A. Pietropaolo, M. Pillon, L. Quintieri, A. Santagata, P. Valente, Italian neutron sources, The European Physical Journal Plus, November 2014, 129:255 6) A.Grossi, L.Quintieri, Misura del rateo di fluenza neutronica termica del pozzetto termico del laboratorio di metrologia delle radiazioni ionizzanti, Report UTFISST-REANUC/RT, (2014). 7) M. Amendola, S. Loreti, R. Remetti, M. Capogni, P.L. Carconi, M.L. Cozzella, P.De Felice, A. Fazio & F. Pisacane. Experimental and Monte Carlo simulation on new manganese bath facility for absolute neutron source emission rate measurement at ENEA_INMRI. Journal of Radioanalytical and Nuclear Chemistry 301, , (2014). Pag. 7/8

8 8. REFERENCES CCRI(III)/15-XX [1] Laitano, R.F., Raponi, F., Rotondi, E., Confronti internazionali effettuati dal CNEN nel campo della metrologia dei neutroni, Proceedings of a national conference: XXI Congresso Nazionale AIPR, Palermo 1979 (1979). [2] Rotondi, E., Raponi, F., Ceravolo, L., Gentilin, P., Ientile, P., Mancini, S., Rondanina, A., I risultati dell'enea nel confronto internazionale organizzato dal BIPM per la misura del flusso di neutroni di una sorgente di Californio, ENEA Tecnical report RT/PAS/87/3, ENEA, Roma (1987). [3] Rotondi E., Calibrazione assoluta di una sorgente di neutroni Am-Be mediante il metodo del bagno al solfato di manganese, Report CNEN-RT/PROT(73)36 (1973). [4] M. Amendola, S. Loreti, R. Remetti, M. Capogni, P.L. Carconi, M.L. Cozzella, P.De Felice, A. Fazio & F. Pisacane. Experimental and Monte Carlo simulation on new manganese bath facility for absolute neutron source emission rate measurement at ENEA_INMRI. Journal of Radioanalytical and Nuclear Chemistry 301, , (2014). [5] Rotondi E., The Thermal neutron flux density standard at C.S.N.: design and calibration, Report CNEN-RT/PROT(73)37, (1973). [6] Laitano R.F., Rotondi, E., Risultati di un confronto fra lo standard di densità di flusso di neutroni termici del C.S.N. Casaccia (CNEN) e quello del P.T.B. di Braunschweig (R.F.T), Report CNEN-RT/PROT(74)36, (1974). [7] A.Grossi, L.Quintieri, Misura del rateo di fluenza neutronica termica del pozzetto termico del laboratorio di metrologia delle radiazioni ionizzanti, Report UTFISST-REANUC/RT, (2014). Pag. 8/8